Electric arc welders, sometimes referred to as "stick welders," are specific types of electrical generators used for joining pieces of metal together. Patents incorporating technology relating to arc welders include U.S. Pat. Nos. 5,317,999 (Kern et al.); 5,376,877 (Kern et al.); 5,489,811 (Kern et al.); 5,497,735 (Kern et al.); 5,504,417 (Kern et al.) and 5,537,025 (Kern et al.), all of which are assigned to the same assignee as this invention.
In arc welding, metal joining is by initially "striking an arc" and thereby passing an electrical current through a thin, stick-like welding rod. The electrical current melts the tip of the rod and, gradually, the rod is consumed in the process. That is, the rod is consumed because it is "laid down" in a molten bead of weld material which quickly hardens to form the welded joint. Rods used in arc welding are formulated using a variety of materials and are made in a variety of diameters, all for specific applications.
The general principle of operation of an arc welder involves applying a voltage potential across a clamp which grips the work piece (actually, one of two pieces to be joined together) and an electrode holder which grips one end of a weld rod. So long as the weld rod does not touch the work piece and complete the electrical circuit, no current flows. But when the rod is touched to the work piece to start current flow, the resulting arc creates sufficient heat to melt the rod and weld the pieces together.
While known arc welders have been and are generally suited for the intended purpose, they are not without disadvantages. One such disadvantage often evidences itself at the start of the welding process, especially when the work pieces are at ambient temperature.
To start the welding process, it is necessary to touch the work piece with the cold, not-yet-molten tip of the rod in order to strike or create the arc, the heat of which progressively melts the rod. And to form a weld of high integrity, the rod must be held so that the portion of such rod which has become molten flows onto and bonds to the pieces to be joined.
To put it in different terms, that extremity of the rod not yet melted must not touch the work piece but, rather, must be maintained at a short distance from such work piece. This is so since it is only in this way that the arc can be sustained. The arc produces high localized heat generally according to the formula I.sup.2 R where I is the value of the current flowing through the rod and the arc and R is the electrical resistance across the arc.
Reconciling the seemingly-inconsistent requirements of touching the rod to the work piece to strike an arc and holding the rod a short distance from the work piece during welding takes a good deal of skill and practice. An operator, especially a less-experienced one, is not always successful in doing so.
When the operator is unsuccessful in striking and maintaining an arc, the rod tip fuses or sticks to the work piece. In that event, the rod must be broken away from the work piece and an arc struck anew. And almost invariably, an undesirable and unsightly spot of metal is left on the work piece. Known welders do not offer a satisfactory solution to this problem.
Other disadvantages of known arc welders relate to size and weight. Their size-to-rated-current and weight-to-rated-current ratios are undesirably high. To put it more in the vernacular, they are large and heavy for the rated current they provide. And increased size and weight usually translate into higher cost.
These undesirable attributes arise at least in some part because earlier workers in this field have not fully appreciated how to use available space most advantageously. For example, aspects of the invention disclosed herein involve what might be described as a "triple duty" or multiple-purpose cooling apparatus. Other aspects involve what might be described as a "high-density" stator that combines several different windings in a very compact arrangement.
Yet another disadvantage of known arc welders relate to ambient noise. When the generating section of the welder is powered by an internal combustion engine, it is not unusual to run the engine at rated speed, even though the power output required of the welder is very substantially less than the available engine horsepower at such speed. Of course, an engine running at rated speed produces more noise than one running at some intermediate speed.
A companion disadvantage of known arc welders relates to engine life. An engine which runs at rated speed during substantially all of its operating life will not last as long as one which runs at some intermediate speed during at least a part of such operating life.
The specification describes creative innovations which address the above-described disadvantages in unique ways.